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UBC Theses and Dissertations
Sedimentary rock hosted copper mineralization in the Neoproterozoic Redstone Copperbelt, Northwest Territories, Canada Milton, Jack Edward
Physical-chemical fluid evolution, timing of fluid-migration and driving forces for fluid-flow are factors that fundamentally control the mass transport that leads to the formation of sedimentary rock hosted copper deposits. This thesis constrains these factors for Kupferschiefer-type mineralization in a sequence of Neoproterozoic rocks of the Redstone Copperbelt, Mackenzie Mountains, Northwest Territories, Canada. Stratiform copper mineralization is located in rift-basins that formed during the break-up of the supercontinent Rodinia within a period of Earth’s history that witnessed evolution of Precambrian life and dramatic climate changes associated with the Snowball Earth glaciations. A U-Pb zircon date is presented, constraining the eruption of a marker unit within the Neoproterozoic sequence that heralded the prolonged period of rifting that led to supercontinent fragmentation. The age also constrains the deposition of the host rocks for stratiform copper mineralization. Dating monazite grains associated with mineralization at the Coates Lake stratiform copper deposit demonstrates that mineralization occurred ~100 My after host rock deposition, following 2-4 km of burial. Mapping, fluid inclusion, paragenetic, and S-Sr-O-C isotope evidence show that mineralizing fluids were ~190 to 250 °C, had salinities of ~32 wt. % NaCl equivalent, were overpressured and circulated through red-beds that underlie mineralization. Fluid-pathways have been traced through the red-beds, up basin-margin faults and back laterally along stratigraphy in mineralized zones, suggesting that flow was circulatory and evidence is presented for free-convection. Two significant glacial episodes may have produced cryogenic brines that are a potential source of salinity for mineralizing fluids. Modelling the behavior of H-O-Cu-S-Cl over a range of temperature and salinity representative of stratiform copper mineralization suggests that significant solubilities of copper can be attained by even weakly oxidized fluids. This study contributes to a growing body of evidence that Kupferschiefer-type deposits are not only formed during early-diagenesis, but can form after significant periods of burial from saline, moderate temperature fluids that are not highly oxidized. A separate style of ‘vein-vug’ copper mineralization has been dated and occurred later in the basin-history, possibly as remobilization of stratiform mineralization; vein-vug mineralization may have formed in association with regional Zn-Pb mineralization across the northern Canadian Cordillera. Supplementary video material is available at: http://hdl.handle.net/2429/54234
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Attribution-NonCommercial-NoDerivs 2.5 Canada